An infrastructure wireless network, such as one complying with the IEEE 802.11-2007 standard, typically comprises one or more stations communicating with an Access Point (AP). The AP transmits a beacon signal to identify itself to stations. A station associates with the AP in a Basic Service Set (BSS) which is also referred to as an infrastructure network. The stations use applicable medium access protocols, such as the distributed coordination function (DCF) based on Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA), the Enhanced Distributed Channel Access (EDCA), and the Hybrid Coordination Function (HCF) Controlled Channel Access (HCCA), as specified in IEEE Std. 802.11-2007, to gain medium access. The stations receive contention parameters from the AP's beacon and apply those parameters to perform CSMA/CA for medium access. As part of HCCA, the AP may also provide polling access for stations.
In an ad hoc wireless network, as also specified in the IEEE 802.11 standards, the stations do not associate with an AP, but instead communicate directly with one another in an Independent Basic Service Set (IBSS) which is also referred to as an ad hoc network. The stations transmit beacons based on a simplified version of CSMA/CA, which allows itself and other stations to use CSMA/CA or EDCA to contend for medium access in the ad hoc network. The stations do not receive contention parameters in the beacons, but apply default contention parameters to perform CSMA/CA.
In known wireless networks, separate procedures for medium access are used for infrastructure and ad hoc networks. Stations are also subject to certain fundamental constraints. For example, a station cannot communicate simultaneously with an AP and another station, unless they all belong to an infrastructure network. Otherwise, a user needs to perform a manual configuration change to enable the station to communicate with the AP or with another station, one at a given time.
According to the IEEE Std. IEEE 802.11-2007, a station transmits when it gains medium access. The station gains medium access when its backoff counter reaches zero if the station uses the DCF, or when one of its access category backoff counters reaches zero if the station uses EDCA. The station also gains medium access if it is granted a polled transmission opportunity (TXOP) through HCCA. Moreover, if a station gains medium access by DCF, it transmits one frame only; if the station gains medium access by EDCA or HCCA, it transmits one or more frames to an AP or a peer station, but not both. The air time must not exceed the explicitly or implicitly specified TXOP duration. In a TXOP obtained for an access category through EDCA, the frames transmitted must also have at least the user priority mapped to that access category.